Introduction to Flask

Basics

• Abdul from Pythonist introduces Flask
• Flask: a micro web framework written in Python
• No enforced dependencies or project layout
• Initially simple, but scalable for complex applications
• Extensions available to add functionality

Setting Up Flask

Virtual Environment

1. Install virtualenv package: pip install virtualenv
2. For Mac users: brew install virtualenv
3. Create a virtual environment: virtualenv <env_name> <python_version(optional)>
4. Activate the virtual environment:

   source <env_directory>/bin/activate
   

Installing Flask

• Install Flask: pip install flask
• Verify installation: pip freeze
• Check import in Python interpreter:

  import flask
  

Building a Simple Flask Application

Creating the App

1. Create a file app.py
2. Import Flask and create an instance:

   from flask import Flask
   app = Flask(__name__)
   

3. The application instance is an object of class Flask
   • Uses WSGI (Web Server Gateway Interface)
   • __name__ is typically the correct value for the application instance constructor

Defining Routes and View Functions

• Routes: URLs mapped to functions
• View Functions: Code executed when a specific URL is accessed
• Define a route with app.route decorator:

  @app.route('/')
  def index():
      return 'Hello, World!'
  

• Basic application created to handle requests to the root URL (/)

Conclusion

• Learned Flask basics:
  • What Flask is
  • Setting up virtual environment
  • Installing Flask
  • Creating a basic application with routes and view functions
• More to explore in upcoming videos